The boiler fireboxes determine what fuel is used- solid fueled fireboxes can run on anything that is capable of burning in a furnace(mostly coal or charcoal are the viable options, BoP ash from the nether could also be used if you don't mind digging) while liquid fueled fireboxes run off certain flammable liquids (creosote oil, lava, diesel, and oil, though of these the only one you'll want to use is probably creosote). These consist of a single base layer of boiler fireboxes, over which between 1 and 4 layers of boiler tanks are placed, depending on the size (look on the tooltip for a list of viable sizes). These are multiblock boilers, and can be 1x1, 2x2, or 3x3, and up to 5 blocks tall. Next are the Railcraft boilers, available at the start of LV. These require a constant source of lava, which is generally not something available at LV, so these are not recommended for use in constant power generation. High Pressure Lava Boilers produce 600 L/s of steam, or 15 EU/t, and run off lava. Like the Small Coal Boilers, these run off coal or charcoal. High Pressure Coal Boilers produce 300 L/s of steam, a much better number, but still only equivalent to 7.5 EU/t. The Simple Solar Boiler produces the same amount of steam, but runs off sunlight, and slowly calcifies, requiring it to be broken and replaced to be restored to its full 120 L/s production. This is the first boiler available, consuming coal or charcoal, and is not really viable for power production, giving a measly 120 L/s of steam, or 3 EU/t of power, or even less with efficiency losses from turbines. Included in this lineup are the Small Coal Boiler. All of these are available at the start of LV.
The first set of boilers available are the small Gregtech boilers.
If a boiler runs out of water, and is then fed more water while it is still hot, it will explode, so make sure you've got enough water production for your boilers! 2L of steam makes 1 EU, multiplied by the efficiency loss of the steam turbine. All boilers require 1L of water per 150L of steam produced. Production: Steam is produced in many boilers, of various types. It can be used through EV, through various sets of gradually better boilers and turbines, however is generally not recommended to be used past MV. It is available as soon as you enter LV, being the only source of power available at the very start. Steam is the first power source you have access to and, as such, is simple to use but not really the best option, especially later on.